The Hevea plant or tree (also called Hevea brasiliensis or a rubber tree) is a well-known source of natural rubber (also called polyisoprene). Rubber sources such as Hevea brasiliensis, Ficus elastica (India rubber tree) and Cryptostegia grandiflora (Madagascar rubbervine) produce natural rubber in the form of a sap where the rubber is suspended in an aqueous solution that flows freely and can be recovered by tapping of the plant. Various non-Hevea plants are also known to contain natural rubber, but their rubber is stored within the individual cells of the plant (e.g., stems, roots or leaves) and cannot be accessed by tapping but can only be accessed by breaking down the cell walls by physical or other means.